The present invention relates to the determination of a diagnostic for a breakdown in an avionic system, and more particularly to a process and device for determining a diagnostic for a breakdown of a functional unit in an on-board avionic system.
The purpose of the diagnostic is to guide a maintenance operator in repairing the avionic system, or in other words in restoring the airplane to normal operation.
The diagnostic may be worked up by a maintenance system on board the airplane or by a maintenance system on the ground.
Avionic systems are composed of a set of functional units such as, for example, calculators, cabling, sensors, applications. These functional units are known as replaceable entities in an airplane, and are also called LRU (“Line Replaceable Unit” in English terminology). The functional units that participate in one and the same function in the avionic system are grouped within systems, and each functional unit belongs to only one single system.
There are known on-board maintenance architectures in which each system is provided with a surveillance unit, also known as BITE (“Built In Test Equipment” in English terminology), which is responsible for surveillance of one or more functional units as well as the functional units connected to this system.
According to these architectures, the different surveillance units rely on surveillance devices, also known as “monitoring” devices in English terminology, which, on the basis of detected symptoms, work up a local diagnostic explaining these symptoms.
This local diagnostic is made up of a certain number of unitary diagnostics, which are associated with a suspect functional unit if the detected symptoms can be explained by the failure of a functional unit, or with several suspect functional units if the symptoms can be explained by the simultaneous failure of several functional units.
An example is illustrated in FIG. 1.
According to this example, a functional unit A (LRU A) receives datum x from functional unit B (LRU B), and this datum x is produced by functional units C (LRU C) and D (LRU D).
Thus, according to this example, if functional unit A no longer receives the data x, then the surveillance unit of the system to which functional unit A belongs will emit the following local diagnostic:
LRU A or LRU B or (LRU C and LRU D)
Thus this local diagnostic is composed of three unitary diagnostics, or in other words LRU A, LRU B and (LRU C and LRU D).
The number of unitary diagnostics is directly related to the ability of the surveillance unit to isolate or not isolate the breakdown.
In the example under consideration, the surveillance unit was not able to determine whether the symptom “functional unit A no longer receives datum x from functional unit B” is due to a failure of functional unit A, which is the data acquisition unit or of functional unit B, or to a double failure of functional units C and D.
Thus, according to these on-board maintenance architectures, when a functional unit suffers a breakdown, several surveillance units detect this failure, and each sends a local diagnostic to a central maintenance system, also known as CMS (“Centralized Maintenance System” in English terminology).
According to a known central maintenance system, this attempts to correlate the different local diagnostics with one another in such a way as to choose one of the local diagnostics, also known as “originating message”, which best reflects the breakdown that originated the different correlated local diagnostics.
Thus, according to these on-board maintenance architectures, the precision of the diagnostic is related firstly to the choice of the local diagnostic and secondly to the number of unitary local diagnostics emitted from the originating message.
Nevertheless, these architectures therefore have the disadvantage of emitting a diagnostic that does not have the greatest relevance.